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| To: | "Laurence KL1X" <[email protected]> |
|---|---|
| Subject: | LF: These sliding doors again |
| From: | "Laurence KL1X" <[email protected]> |
| Date: | Mon, 21 Aug 2006 20:38:16 -0800 |
| Delivered-to: | [email protected] |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
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Considering the extenuative affects to kill common mode qrm coming from inside the room, up the coax and out Ive been playing to try to find out whats what. Yep an Im using isolating toroids and all that guff. Here we go For a merit test I "built" my own 4 x 3 metre flexible doorway in an area similar but without the metal frame being there. This was with one continuous length of folded aluminum foil some 4 cms in width and a couple of thicknesses to give it some mechanical strength with all that tugging - and some 14 metres in circumference. I compared the extenuative results of common in building noise with the one with a known killer of QRN my favorite sliding balcony door frame - At 137 Khz the door frame gave appx 30-40dB of noize attenuation (nice) my aluminum made up version standalone 4dB... or less. Open circuiting the aluminium made up little difference So I pondered - I knew from testing in Singapore that the metal frame in my hotel that worked so well wasn't connected to "mains" earth - but what about this one here in Shanghai? - Measured it and hey presto it is, and low Z too, certainly less than 1 ohm - theyve added a Earth safety strap somewhere and all the buildings doorways and sliding doors on the balconies are all boded together at "building earth" (notice Im not saying radio) potential and defacto we have a screened box - with my eprobe poking out of one side and the screen connected to that box. So this left the question of what was happening in Singapore? - Ive found out that the sliding door frame is connected to the steel work of the building but for some reason there is No connection to the mains earth in the 220vac supply - I actually think this is a bit dodgy but heck that mains earth was hot with RF and brought the noise up by 30dB, here luckily in Shanghai it doesn't. Choosing the right balcony sliding door for your probe has merits - the one on the North side cuts the noize out but then I get pylon hash, the one on the southside is much quieter but now screened from Asia/Americas and Eu - but I can still see DCF39 So no tuned loops, tooned earths, counterpoises or what ever just a screened metal box that keeps the rubbish mostly inside. Mostly. As Ive seen before if I was on the top floor its works pretty well for rx if i can get my probe above the roof line but Im on floor 3 out of 12 and by pushing the probe out further and further away from the building makes a huge difference - more than 1 S point per metre at 200Khz on some of the local NDB's. I have a cunning plan (as one famous actor said once "so cunning if you put a tail on it, you would call it a fox"), to get some form of earth into the ground and extend is camouflaged up the side of the building. If it works it will be interesting to see what if any affect is has on the qrm, if it doesn't Ill probably be in jail. Laurence, KL1X in BY, enroute tomorrow to KL7
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